Practical Method and Novel Mechanism for Optical Resolution of BINOL by Molecular Complexation with N-Benzylcinchoninium Chloride

A highly efficient and practical resolution of racemic 1,1′-bi-2-naphthol (BINOL) has been achieved through molecular complexation with N-benzylcinchoninium chloride, which can be readily prepared in 85% yield using an improved procedure through the reaction of cinchonine with benzyl chloride in dimethylformamide (DMF). It is found that the absolute configuration of BINOL included in the molecular crystals is R, which is the same as in the case of using N-benzylcinchonidinium chloride. This result is discussed in terms of molecular recognition in the solid state. X-Ray structural analysis of molecular crystal formed between (R)-BINOL and N-benzylcinchoninium chloride indicates that the additive effect of the chiral features of the host, the interaction pattern between the functional groups of the host and guest, and the complementary molecular packing in the crystal lattice dominates the stereochemistry of the guest in the molecular crystal.